1. Field of the Invention
This invention concerns threaded inserts of the type adapted to be secured to an anchoring structure.
2. Description of the Prior Art
Threaded inserts of the type formed of hardened steel and adapted to be anchored in an anchoring structure of softer material such as aluminum have been widely used in such applications as aircraft structures and similar structures formed of materials such as aluminum or plastic having inadequate hardness to directly receive threaded fasteners, particularly the fine pitch machine threads. These threaded inserts typically are adapted to be threaded into a bore in the anchoring structure and then locked into position by means of a serrated locking ring which is adapted to mate with the threaded insert and to be forced into the surrounding anchoring structure causing cold flow of the anchoring structure material so as to secure the locking ring and thereby the insert against rotation in the anchoring structure. The serrations provide a means for allowing the forcing of the locking ring into the surrounding anchoring structure material by cold flow and also allow for relatively great torsional strength between the locking ring and the threaded insert. The cold flow of the anchoring structure material firmly secures the locking ring in position to prevent it from becoming dislodged.
An alternative approach disclosed in U.S. Pat. No. 3,270,792 involves the use of keys located at the periphery of the insert and adapted to be forced through corresponding slots in the insert and deform the surrounding threads to provide the locking function.
A drawback to these arrangements exists in that no practical, easily implemented technique is possible for removing an insert so as to allow replacement, as for example with another insert having a differing size threaded bore; or to remove a broken bolt. This drawback is created by the small cross-sectional area and location of the locking rings and keys making engagement with removal tools difficult. In the case of locking rings, even if the locking ring could be removed, the serrations of the locking ring on the new insert may not be firmly secured due to the presence of the old impressions left by the locking ring of the original insert. Thus, drilling out of the old bore and replacement with a larger size insert would be necessary.
Therefore, the object of the present invention is to provide such a threaded insert which is easily removable and replaceable with another insert of the same size, without compromising the effectiveness of either the original or the replacement installation.